'J>! 


UNIVERSITY   OF   CALIFORNIA 

AGRICULTURAL    EXPERIMENT    STATION 

E.    W.    HILGARD,    Director 


CIRCULAR 


BROWN  ROT  OF  STONE  FRUITS. 

By  Frederic  T.  Bioletti. 


Brown  Rot  is  one  of  the  most  serious  diseases  with  which  fruit- 
growers have  to  contend.  It  attacks  principally  stone  fruits — peaches, 
plums,  apricots,  and  cherries,  but  occasionally  does  damage  to  apples, 
pears,  and  quinces.  It  is  widely  distributed  throughout  Europe  and 
the  United  States.  In  some  of  the  Eastern  States  it  is  considered  the 
most  destructive  disease  with  which  the  peach-grower  has  to  contend. 
In  Delaware  and  Georgia  it  often  destroys  from  25%  to  75%  of  the 
crop.  It  is  reported  to  destroy  more  peaches  and  cherries  in  Michigan 
than  all  other  diseases  combined.  In  Kentucky  it  is  said  to  be  very 
destructive  to  apples,  and  in  Oregon  it  has  been  the  cause  of  very 
serious  losses  to  the  prune- growers  for  several  seasons.  In  California, 
though  its  occurrence  has  been  noted  for  several  years,  no  serious 
damage  seems  to  have  been  occassioned  until  last  year,  when  it 
appeared  abundantly  in  several  localities.  Statements  were  received 
from  prune- growers  in  Napa  County  that  50%  of  the  crop  was  rotting 
in  some  orchards,  and  specimens  of  the  diseased  fruit  received  by  the 
Agricultural  Station  at  Berkeley  showed  Brown  Rot  to  be  the  cause. 
In  several  large  orchards  in  Alameda  County  the  late  varieties  of 
apricots  were  seriously  affected;  25%  or  more  of  the  crop  being 
destroyed  in  some  cases.  All  the  cases  of  this  disease  which  have  so 
far  been  brought  to  the  notice  of  the  Station  have  been  in  localities 
not  far  from  the  sea  and  therefore  more  or  less  under  the  influence  of 
the  summer  sea  fogs.  As  there  seems,  however,  to  be  a  tendency  of 
the  disease  to  spread  in  California,  and  as  recent  experiments  in 
Georgia  and  elsewhere  show  that  it  can  be  controlled  with  comparative 
ease,  the  following  brief  description  of  the  disease  and  of  the  method 
of  treatment  is  given. 

Brown  Rot  is  caused  by  a  mould  or  fungus  called  Monilia  fructigena, 
which  attacks  various  parts  of  the  plant,  leaves,  blossoms,  twigs,  and 
fruit.  Its  effects  are  most  evident  upon  the  fruit,  but  it  does  an 
amount  of  damage  that  is  hard  to  estimate,  by  attacking  the  other 


parts  of  the  plant,  but  which  some  observers  consider  to  be  almost 
equal  to  that  of  the  rotting  of  the  fruit.  The  fruit  is  usually  attacked 
after  it  has  attained  full  size  and  just  as  it  commences  to  soften.  The 
first  symptom  in  the  case  of  apricots  and  peaches  is  a  brown  spot  on  one 
side  of  the  fruit.  This  spot  gradually  enlarges  and  becomes  covered 
with  small  ashy-gray  pimples  which  consist  of  myriads  of  the  spores  of 
the  fungus.  Soon  the  whole  fruit  turns  brown  and  the  entire  surface 
becomes  covered  with  spores.  The  fungus  then  passes  from  the 
rotten  fruit  through  its  stem  into  the  twig.  Finally  the  disease 
attacks  the  twig  so  severely  that  it  dries  up,  loses  its  leaves  and  dies. 
The  accompanying  illustration  shows  apricots  and  twigs  in  various 
stages  of  the  disease,  and  the  gradual  progress  from  the  fruit  to  the 
twigs  is  well  shown.     In  the  fruit  on  the  left,  by  looking  closely  it 


■'..-: 


Pacific  Rural  Press. 


EFFECT  OF  BROWN  ROT  ON  FRUIT  AND  TWIGS  OF  APRICOTS. 

can  be  seen  that  the  lower  side  is  darker-colored  than  the  upper,  and 
that  the  light-colored  spores  have  commenced  to  appear.  The  middle 
specimen  is  covered  with  a  layer  of  the  pimple-like  masses  of  spores, 
and  the  leaves  have  commenced  to  wither;  while  in  the  specimen  on 
the  right  the  leaves  are  quite  dead  and  the  fungus  has  passed  into  the 


twig.  The  appearance  of  the  disease  on  plums  and  prunes  is  some- 
what different.  In  none  of  the  specimens  received  at  the  station  were 
the  spores  formed  when  they  arrived.  The  appearance  of  the  diseased 
plums  was  not  at  first  very  different  from  that  of  the  normal  ones,  but 
when  they  were  cut  open  the  inside  was  found  to  be  discolored.  When 
placed  in  a  moist  warm  place,  however,  the  spore  masses  developed  in 
one  or  two  days,  and  then  the  appearance  was  very  similar  to  that  of 
the  diseased  apricots. 

4 

The  attacked  fruit,  instead  of  becoming  soft  and  falling  off,  as 
with  most  other  rots,  gradually  dries  up  and  often  remains  firmly 
attached  to  the  tree  until  the  following  spring.  In  spring  a  new  crop 
of  spores  is  produced  by  the  mummified  fruit,  and,  in  the  case  of 
peaches,  the  young  growth  and  blossoms  are  attacked.  The  same 
probably  occurs  in  the  case  of  apricots  and  other  fruits.  One  of  the 
worst  features  of  this  disease  is  that  the  fungus  may  be  in  apparently 
healthy  fruit.  Peaches  which  when  picked  and  packed  showed  no 
sign  of  the  rot,  may  be  completely  spoiled  when  the  boxes  are  opened 
two  or  three  days  later. 

Treatment. — As  the  fungus  passes  the  winter  principally  upon  the 
mummified  fruit,  the  most  effective  method  of  combatting  the  disease 
is  to  remove  and  destroy  thoroughly  all  the  diseased  fruit.  The 
diseased  apricots  should  be  gathered  and  destroyed  as  soon  as  the 
appearance  of  brown  spots  indicates  that  they  are  attacked,  and  not 
left  on  the  tree  until  the  fungus  has  penetrated  the  twigs.  No  fruit 
should  be  left  on  the  surface  of  the  ground.  Any  fruit  which  falls 
near  the  base  of  the  trunk  should  be  raked  away  in  order  that  it  may 
be  buried  by  the  plow.  These  measures  alone,  thoroughly  applied, 
have  been  sufficient  to  produce  a  notable  diminution  in  the  amount  of 
fruit  attacked ;  but  complete  immunity  can  be  obtained  only  by  proper 
spraying  in  addition.  All  orchards  where  there  is  reason  to  suspect 
the  presence  of  the  rot,  such  as  those  where  it  appeared  last  year  and 
those  in  their  immediate  neighborhood,  should  be  sprayed  with 
Bordeaux  mixture  one  or  two  weeks  before  the  blossoms  open.  This 
will  prevent  the  infection  of  the  blossoms,  and  in  the  case  of  peaches 
will  also  prevent  curl-leaf.  A  winter  wash  with  our  ordinary  lime- 
salt- sulphur  mixture  would  doubtless  be  nearly  as  effective  against  the 
Brown  Rot,  and  where  used  for  destroying  scale  and  other  insects  the 
first  spraying  with  Bordeaux  might  be  omitted.  In  any  case,  where 
the  Brown  Rot  appeared  last  year  the  trees  should  be  sprayed  wTith 
Bordeaux  as  soon  as  the  fruit  has  set.  These  measures  will  in 
most  cases  be  sufficient  with  early  fruit;  but  for  late-ripening  varieties, 
such  as  Moorpark  apricots,  a  third  spraying  should  be  given  about  a 
week  or  ten  days  before  the  fruit  commences  to  color.  As  Bordeaux 
would  stain  the  fruit  at  this  time  it  is  better  to  use  a  spray  of  copper 
acetate. 


Bordeaux  mixture  is  a  fungicide  consisting  of  bluestone  (copper 
sulfate),  lime  and  water,  mixed  in  various  proportions  according  to 
the  season  and  to  the  kind  of  tree  to  be  sprayed.  For  the  first 
spraying,  before  the  buds  have  started,  the  following  formula  can  be 
recommended : 

Copper  sulfate 5  pounds 

Quicklime 5  pounds 

Water 45  gallons 

For  spraying  the  trees  when  in  leaf  it  is  better  to  use  less  sulfate 
and  more  lime,  especially  on  peaches,  in  order  to  avoid  danger  of 
injuring  the  foliage.  For  the  second  and  any  of  the  subsequent 
sprayings  the  following  should  be  used: 

Copper  sulfate 3  pounds 

Quicklime 6  pounds 

Water 45  gallons 

Directions  for  mixing. — 1.  Suspend  the  copper  sulfate  in  a  basket 
or  perforated  wooden  box,  in  a  barrel  containing  half  the  water.  The 
box  containing  the  sulfate  should  be  just  below  the  surface  of  the 
water  in  order  to  dissolve  quickly. 

2.  Slake  the  quicklime  slowly  and  with  great  care  to  insure  a 
perfectly  smooth  paste  free  from  grit.  After  the  paste  has  stood  for 
twenty  to  forty  minutes,  with  enough  water  to  ensure  it  from  drying, 
dilute  with  the  remainder  of  the  water  and  strain  through  a  wire  sieve. 

3.  When  the  sulfate  is  dissolved  and  the  milk  of  lime  quite  cool, 
stir  each  mixture  well  and  pour  them  together  into  a  suitable 
receptacle. 

If  large  quantities  of  Bordeaux  are  needed  it  is  more  convenient  to 
make  up  two  stock  solutions  as  follows: 

A.—  Copper  sulfate,  50  pounds;  Water,  25  gallons. 
B.— Quicklime,  50  pounds;  Water,  25  gallons. 

These  should  be  made  up  in  the  way  already  described  and  separated 
until  needed.  For  use  take  half  a  gallon  of  solution  A  for  every 
pound  of  copper  sulfate,  and  half  a  gallon  of  mixture  B  for  every 
pound  of  lime  wanted;  dilute  each  separately  with  a  little  less  than 
half  the  water;  pour  together  and  make  up  to  the  required  volume 
with  water,  stirring  thoroughly.  Never  mix  the  lime  and  copper 
liquids  when  hot. 

The  spray  should  be  made  as  short  a  time  as  possible  before  using 
and  should  be  applied  when  the  trees  are  dry  and  the  weather  calm. 
Only  the  best  quality  of  quicklime  should  be  used.  The  spray  for 
use  when  the  fruit  is  large  is  made  by  mixing  six  ounces  of  Copper 
Acetate  (dibasic  acetate  of  copper)  with  forty-five  gallons  of  water. 
When  the  acetate  is  quite  dissolved  and  mixed  with  the  water  it  is 
ready  to  be  applied. 


Berkeley,  January,  1901. 


